This invention relates to jet printing apparatus of the type used to apply a printing medium to a moving substrate and a method for doing the same.
There has for some time existed a need in the packaging arts for a simple and reliable device to label boxes, containers, and the like, which are moving past a printing station on a conveyor. Ink jet printing devices have been used to accomplish this task and typically comprise a plurality of nozzles through which ink can be selectively ejected onto the moving container to produce alpha-numeric characters. Such known devices have generally employed either piezoelectric ejector means associated with each nozzle for ejecting ink or an electrically operated needle valve or plunger for opening and closing each nozzle. In either case, the device employed is relatively complex and can only print larger sized alpha-numeric characters, e.g., characters having a height of from 13 mm to 70 mm.
The height limitation of the characters which can be printed is limited by the size of the nozzle orifice through which ink is ejected and by the size of the valve employed. In prior devices, there was a lower limit to the orifice sizes which could be employed due to the fact that the inks employed tended to clog orifices below a given diameter. Another disadvantage of the devices which selectively meter ink through a valve lies in the fact that the more exotic inks, many of which have desirable printing characteristics, are often incompatible with the valve components. The use of such inks results in destruction or greatly diminished service life of the valve.